Recall from Chapter 18 that
the PostgreSQL server provides a
large number of run-time configuration variables. You can set
database-specific default values for many of these settings.

For example, if for some reason you want to disable the
GEQO optimizer for a given
database, you'd ordinarily have to either disable it for all
databases or make sure that every connecting client is careful to
issue SET geqo TO off. To make this
setting the default within a particular database, you can execute
the command:

ALTER DATABASE mydb SET geqo TO off;

This will save the setting (but not set it immediately). In
subsequent connections to this database it will appear as though
SET geqo TO off; had been executed just
before the session started. Note that users can still alter this
setting during their sessions; it will only be the default. To
undo any such setting, use ALTER DATABASE
dbname RESET varname.

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